I wouldn’t recommend hard coding in some enumerations for year selection. As you stated it should only ever show the current year and the next. Therefore every year you would have to change these manually and redeploy.
You could setup a scheduled event to change two records of an entity YEAR every year or setup a page in admin to do this.
If you only want to show the year you can use formatDateTime($DateAttribute,’YYYY’)
A better option to show years without enumeration is to create an entity ‘Year’ with and attribute ‘Year’. Create the objects using a Microflow or just create a grid and mannualy create the years that you need.
Associate your object with the Year entity and now you can use the reference selector drop-down.